linux-kernel - Re: [PATCHv6 11/17] mm/hugetlb: Remove fake head pages

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Message-ID: <110aedf7-9f31-4552-b772-395433d7bdb3@gmail.com>
Date: Sat, 7 Feb 2026 22:50:47 +0000
From: Usama Arif <usamaarif642@...il.com>
To: "David Hildenbrand (Arm)" <david@...nel.org>,
 Kiryl Shutsemau <kas@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>,
 Muchun Song <muchun.song@...ux.dev>, Matthew Wilcox <willy@...radead.org>,
 Frank van der Linden <fvdl@...gle.com>
Cc: Oscar Salvador <osalvador@...e.de>, Mike Rapoport <rppt@...nel.org>,
 Vlastimil Babka <vbabka@...e.cz>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Zi Yan <ziy@...dia.com>,
 Baoquan He <bhe@...hat.com>, Michal Hocko <mhocko@...e.com>,
 Johannes Weiner <hannes@...xchg.org>, Jonathan Corbet <corbet@....net>,
 Huacai Chen <chenhuacai@...nel.org>, WANG Xuerui <kernel@...0n.name>,
 Palmer Dabbelt <palmer@...belt.com>, Paul Walmsley
 <paul.walmsley@...ive.com>, Albert Ou <aou@...s.berkeley.edu>,
 Alexandre Ghiti <alex@...ti.fr>, kernel-team@...a.com, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
 loongarch@...ts.linux.dev, linux-riscv@...ts.infradead.org
Subject: Re: [PATCHv6 11/17] mm/hugetlb: Remove fake head pages



On 07/02/2026 21:25, David Hildenbrand (Arm) wrote:
> On 2/7/26 21:16, Usama Arif wrote:
>>
>>> +
>>>   int __meminit vmemmap_populate_hvo(unsigned long addr, unsigned long end,
>>>                          int node, unsigned long headsize)
>>>   {
>>> +    unsigned long maddr, len, tail_pfn;
>>> +    unsigned int order;
>>>       pte_t *pte;
>>> -    unsigned long maddr;
>>> +
>>> +    len = end - addr;
>>> +    order = ilog2(len * sizeof(struct page) / PAGE_SIZE);
>>
>>
>> This doesnt work for ARM. For len = 32 (2MB contiguous-PTE hugetlb on arm64):
>> ilog2(32 * 64 / 65536) = ilog2(2048 / 65536) = ilog2(0) which is undefined.
> 
> HVO should not be possible for that size, and we should never reach that point, no?
> 
> Remember that for HVO, the metadata must span at least two pages.
> 

Ah yeah thats right, ignore me. Its also checked in hugetlb_vmemmap_optimizable_size,
so its all good.